1. Field of the Invention
This invention primarily relates to a vacuum type booster device for boosting the master cylinder of hydraulic power brakes, clutch or the like of an automobile by means of a vacuum force. More specifically, the present invention relates to a vacuum type booster device of the kind in which a booster piston is axially slidably accommodated in a booster shell and a diaphragm is superposed on the rear surface of a disc portion of the booster piston, the diaphragm having an inner circumferential bead connected to the booster piston and an outer circumferential bead connected to the circumferential wall of the booster shell, the booster piston and diaphragm together dividing the interior of the booster shell into a front side first working chamber in communication with a vacuum supply source and a rear side second working chamber selectively in communication with the first working chamber or the atmosphere via a control valve operatively connected to an input member; the front and rear walls of the booster shell are connected to each other by tie rods extending through the disc portion of the booster piston and through the diaphragm; and seal means are provided for through-holes in the disc portion through which the tie rods extend.
2. Description of the Prior Art
The booster device as described above is used in such a manner that the rear ends of the tie rods are fixed to the vehicle body serving as the support wall and the master cylinder is fitted to the front ends of the tie rods. The booster device is, during its operation, capable of transmitting a forward thrust load, applied from the booster piston to the master cylinder, to the support wall via the tie rods and is thus capable of preventing the load from acting upon the booster shell. Accordingly, the booster device of this kind has the advantage that the booster shell need not have such a high rigidity as to withstand the load and so can be formed from thin steel sheet, synthetic resin or the like material, thereby reducing the total weight of the booster device.